Police officers have been accused of using Tasers to inflict pain to gain compliance, a report by the police watchdog says. Concerns are also raised about the use of Tasers on suspects already in custody, in the findings by the Independent Police Complaints Commission.

Police use of Tasers is controversial. They can be used to fire barbs that deliver an electric current, subduing a suspect. They can also be used in "drive-stun" mode, to apply a shock directly to the body. The report says: "The IPCC has major concerns about the use of Tasers in 'drive-stun' mode, where the Taser is applied directly to the body without a cartridge rather than fired from a distance."

It adds: "There is a risk, given the increase in Taser use, that police officers could become increasingly reliant on using force to gain compliance. This is particularly apparent in drive-stun mode."

The watchdog calls for reforms in guidance and training, and notes use of "drive-stun" by officers can occur when they are grappling with suspects and thus are too close to fire a Taser's barbs.

IPCC commissioner James Dipple-Johnstone said: "When used in this way it is purely a means of pain compliance. Yet in several of the cases we reviewed, where it was used for the purpose of gaining compliance, it had the opposite effect, stimulating further resistance."

The report says the IPCC has particular concern about the use of Tasers on those already in custody: "The IPCC believes that this is only justifiable in exceptional circumstances, taking into consideration the controlled nature of the custody environment."

The report says that in two cases people with epilepsy were Tasered, causing one person to have a seizure, while another who struck by electric current while having a seizure.

In two cases officers fired Tasers at innocent people who had been wrongly identified as suspects, and in one case a suspect turned a person into a "human shield" when confronted by an officer armed with a Taser, with the result the innocent passer by was struck by the current.

The report notes, and police maintain, Taser use saves lives and can mean officers are less likely to have to resort to firearms, but raises concerns about their use on young and mentally ill people.